Calcium ions initiate the selective depolymerization of the pellicular microtubules in bloodstream forms of...

Calcium ions (100 microM) were found to initiate the selective and complete depolymerization of the pellicular microtubules of Trypanosoma brucei. The Ca2+-dependent release of tubulin was found to occur without the detectable mediation of calmodulin. The released, depolymerized, pellicular tubulin from T. brucei cross-reacted with a monoclonal antibody raised against yeast tubulin. The pellicular tubulin was found to be composed of two alpha isotypes (apparently equal amounts) and one beta isotype. No other proteins were released from the plasma membrane-microtubule complexes during treatment with Ca2+. The released pellicular tubulin was capable of reassembly into microtubules with normal ultrastructure. The observations reported here suggest that a special process may be required to accommodate the cleavage furrow during cytokinesis. This process would either be the Ca2+-dependent depolymerization of at least two of the cross-linked pellicular microtubules or the detachment of the cross-bridges between two pairs of pellicular microtubules on opposite sides of the cell.